Appetite suppression with dopamine-fatty acid conjugates

ABSTRACT

The invention involves the formation of a prodrug from a fatty acid carrier and a neuroactive drug. The prodrug is stable in the environment of both the stomach and the bloodstream and may be delivered by ingestion. The prodrug passes readily through the blood brain barrier. Once in the central nervous system, the prodrug is hydrolyzed into the fatty acid carrier and the drug to release the drug. 
     In a preferred embodiment, the carrier is 4,7,10,13,16,19 docosahexa-enoic acid and the drug is dopamine. Both are normal components of the central nervous system. The covalent bond between the drug and the carrier preferably is an amide bond, which bond may survive the conditions in the stomach. Thus, the prodrug may be ingested and will not be hydrolyzed completely into the carrier molecule and drug molecule in the stomach.

BACKGROUND OF THE INVENTION

This invention relates in general to the fields of medicine,pharmacology and biochemistry, and more particularly to prodrugs capableof delivering a drug across the blood brain barrier including a prodrugmade of a fatty acid-dopamine conjugate that is effective as anappetite-suppressant.

There are many obstacles to developing treatments which allow thedelivery of a drug to an active site in the body. Ingestion of a drugoften is not possible because many drugs will not survive theenvironment of the stomach. Thus, easy and safe self-administration ofmany drugs is not available. A drug, of course, may be injected directlyinto the blood stream of a patient. However, because some drugs do notsurvive for very long in the bloodstream, frequent injections at greatinconvenience to a patient may be necessary. The inability of a drug tosurvive in the bloodstream may be overcome in certain instances byincreasing the dosage or by increasing the frequency of administration.However, increasing the dosage can result in undesirable side effectsand increasing the frequency of administration only adds inconvenience.

The delivery of a neuroactive drug to the central nervous system (CNS)via the bloodstream involves an extraordinary obstacle; the drug must becapable of crossing the blood brain barrier. The blood brain barrier mayloosely be regarded as a biological exclusion barrier involving bothpassive and active transport, which barrier controls the exchange ofmaterials between the plasma and the central nervous system. Many drugsubstances are unable to pass through this barrier in efficaciousamounts or at all. Thus, there is a serious need for a mechanism forintroducing a drug across the blood brain barrier and into the CNS.

Efforts have been taken to enhance the ability of certain drugs to passthrough the blood brain barrier. Investigators have attempted to maskthe polar groups of a drug to produce more lipophilic derivatives, aslipophilic compounds are believed to cross the blood brain barrier morereadily than hydrophilic compounds. For example, diacetyl and triacetylesters of dopamine and norepinephrine have been made to mask thehydroxyl groups of these compounds and produce more lipophilicderivatives. This investigator has formed an ester bond betweenγ-aminobutyric acid, a drug which is unable to cross the blood brainbarrier, and a "carrier" molecule having an enhanced ability to crossthe blood brain barrier. The carrier-drug conjugate shares with thecarrier the ability to cross the blood brain barrier. Once in the CNS,the conjugate itself may be active. However, it is believed that theester bond between the carrier and drug is broken in the CNS to releasethe drug in its native form. This may occur due to the general presenceof active, non-specific esterases throughout the CNS.

Appetite-suppressant drugs have been sought for many years. Dopamine isbelieved to be involved in the neuropathways responsible forappetite-suppression. Dopamine itself is not used as anappetite-suppressant because it does not readily cross the blood brainbarrier. Drugs which closely resemble the structure of dopamine andwhich will cross the blood brain barrier have been used with somesuccess as alternatives to dopamine.

The most widely used appetite-suppressant drugs are generally based onderivatives of amphetamine, which structurally resembles dopamine andhas some properties which correspond to a dopamine agonist. Unlikedopamine, sufficient uptake of amphetamines across the blood brainbarrier does occur to produce a biological effect. However, amphetamineshave many serious cardiovascular and neuropsychiatric side effects, aswell as a tendency to develop tolerance, the increasing resistance tothe usual effect of the drug over time. At worst, tolerance to a drugrenders the drug useless. At best, tolerance generally encourages theuse of higher drug doses, increasing the possibility of undesirable sideeffects. In animal tests, tolerance to certain of these amphetaminederivatives has been shown to develop within one day after one dose.Using amphetamine itself, tolerance has been shown to develop within3-15 days.

Dopamine is also known to play a crucial role in several neurologicallyrelated disorders. For example, Parkinsonism is a striatal dopaminedeficiency. Because dopamine (and related catacholamines) does not crossthe blood brain barrier Parkinsonism is treated with L-Dopa, a precursorto Dopamine. This treatment, however, is at the expense of a widevariety of undesireable side effects, including hallucination. Dopamineagonists which are used in the treatment of hyperprolactinemiaassociated with pituitary adenomas or amenorrhea also induceundesireable side effects. Thus, there is a serious need for deliveringdopamine itself or dopaminergic agents directly to the brain.

SUMMARY OF THE INVENTION

The invention involves the formation of a prodrug from a fatty acidcarrier and a neuroactive drug. The prodrug is stable in the environmentof both the stomach and the bloodstream and may be delivered byingestion. The prodrug passes readily through the blood brain barrier.The prodrug has a brain penetration index of at least two times thebrain penetration index of the drug alone. Once in the central nervoussystem, the prodrug, which preferably is inactive, is hydrolyzed intothe fatty acid carrier and the drug. The carrier preferably is a normalcomponent of the central nervous system and is inactive and harmless.The drug, once released from the fatty acid carrier, is active.

Preferably, the fatty acid carrier is a partially-saturated straightchain molecule having between about 16 and 26 carbon atoms, and morepreferably 20 and 24 carbon atoms. Most preferably, the carrier is 4, 7,10, 13, 16, 19 docosahexa-enoic acid. ##STR1## The covalent bond betweenthe drug and the carrier preferably is an amide bond, which bond maysurvive the conditions in the stomach. Thus, the prodrug may be ingestedand will not be hydrolyzed completely into the carrier molecule and drugmolecule in the stomach.

Most preferably, the drug is dopamine, also a normal component of thecentral nervous system and the prodrug is ##STR2## Compound 8739 may beexpressed alternatively as ##STR3## This compound has been found to beuseful as an appetite-suppressant. It has a brain penetration index of33, crossing the blood brain barrier eight times as well as dopamine. Itis a partial dopamine agonist that is inactive until it crosses theblood brain barrier and hydrolyzes to release dopamine into the centralnervous system. The drug suppresses appetite without harmful sideeffects and without inducing tolerance. The prodrug also appears to becapable of delivering the dopamine preferentially into the synaptosomalmembranes, the location of the drug action.

It is an object of the invention to provide an appetite-suppressant drugthat will not induce tolerance and will not cause harmful side effects.

Another object of the invention is to provide a carrier molecule capableof being combined with a drug to form a prodrug that will readily crossthe blood brain barrier and allow release of the drug into the centralnervous system.

Another object of the invention is to provide a prodrug that is stablein the environment of the stomach and in the bloodstream.

Another object of the invention is to provide an amide derivative ofdopamine with biological activity useful in the regulation of appetite.

Another object of the invention is to provide pharmalogical compositionscomprising amides of the carrier of the invention combined withneuroactive drugs, and particularly dopamine.

Still another object of the invention is to provide a method fordelivering a neuroactive drug, including dopamine, to the centralnervous system.

Yet another object of the invention is to provide a method forregulating appetite.

Yet a further object of the invention is to provide a method fortreating neurological disorders in general, and specifically forintroducing dopamine and dopaminergic agents into the brain to treatdopamine related disorders such as Parkinsonism and hyperprolactinemia.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the effect of the prodrug of the preferredembodiment on motor activity and food intake of mice;

FIG. 2 is a graph comparing the effect on mice of varying the mode ofdelivery of the prodrug of the preferred embodiment;

FIG. 3 is a graph showing the effect on mice of long term administrationof the prodrug of the preferred embodiment; and

FIG. 4 is a graph comparing the effect on mice of long termadministration of the prodrug of the perferred embodiment withamphetamine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS AND OF THE DRAWINGS

The most preferred embodiment of the invention is ##STR4## This compoundhas extraordinary and unexpected properties. This compound, hereinaftercalled compound 8739, is a partial dopamine agonist that is inactiveuntil it crosses the blood brain barrier to release dopamine into thecentral nervous system (CNS). Unlike dopamine, compound 8739 survivessufficiently in the environment of the stomach and the bloodstream andtherefore can be administered orally.

Compound 8739 has an enhanced ability to cross the blood brain barrier,with a brain penetration index (BPI) of about 33, as compared to about 4for dopamine. It is inactive as a prodrug in that it does not bind toeither D- 1 or D-2 dopamine receptors. Rather, once in the centralnervous system, dopamine is released as an active fragment of compound8739. In addition, compound 8739 is taken up into the synaptosomalmembranes preferentially, the synaptosomal membranes being the site ofactivity for the dopamine. This property may contribute to thecompound's desirable properties.

Once dopamine is released as an active fragment, it produces effects onfood intake and on general locomotor activity in mice in a dosedependent manner. Food intake decreased by as much as 50% at the higherdoses. Open field activity also decreased by about 50%, indicating that,unlike amphetimine, compound 8739 has a tranquilizing effect rather thanan activity enhancing effect.

Many of the undesirable side effects of amphetamines were absent.Compound 8739 failed to induce "stereotypy", failed to produce an effecton "circling behavior" of striatal lesioned rats, and failed todemonstrate any diverse effects on motor function or motivation in testanimals. Remarkably, there was no indication of tolerance. Failure toinduce tolerance was unexpected.

Another favorable property of compound 8739 was unexpected. Previousreports have demonstrated that fatty acids, including the fatty acid ofcompound 8739, induce swelling of the brain. Chan, P. H., Fishman, R.A., SCIENCE, Vol. 20, 358 360 (1978). Compound 8739 (and another prodrugcompound made from a straight chain fatty acid having 20 carbon atomsand 4 double bonds), however, did not induce any swelling.

Experimental Data Synthesis of the Compound 8739

Compound 8730 is synthesized as follows: ##STR5##

DHA is first converted to DHA anhydride in the presence of dicyclohexylcarbodiimide. This is then reacted with dopamine in the presence ofdimethylaminopyridine as the acid acceptor in tetrahydrofuran. In atypical experiment 300 mg of DHA (0.009 M) was dissolved in a mixture of3 ml hexane and 4 ml benzene and stirred under nitrogen. Next, asolution of 0.00615 M of dicyclohexyl carbodiimide in 4 ml benzene(0.1267 g) was stirred together with the DHA for 3 hr at roomtemperature. A white precipitate of dicyclohexyl urea formed as thereaction proceeded. The dicyclohexyl urea was filtered off to give aclear solution of the anhydride in benzene. This was concentrated downto 2 ml in a rotary evaporator and diluted with 10 ml of tetrahydrofuran(dry). The freshly prepared anhydride was then added to a solution ofdopamine hydrobromide (0.1053 g) (or 0.005 M) in the presence of 0.009 Mof diethylaminopyridine (0.098 g). The initially cloudy mixture afterstirring for 30 min at room temperature gave a mixture of a clear liquidand a brown precipitate. At the end of the reaction, 0.2 ml of water wasadded to the mixture, and stirring was continued for an additional 30min to completely hydrolyze any remaining unreacted anhydride. Theliquid phase was isolated and evaporated to dryness to yield a brownviscous solid. This was then dissolved in 70% ethanol in water (25 ml),and the solution was then passed through a mixed-bed ion exchange resincontaining a strong acidic resin based on polystyrene sulfonic acid anda strong basic resin based on quanternary ammonium substituents such astetramethyl amonimum hydroxide (RG501, Fisher Scientific, Cambridge,Mass.) using 90% ethanol in water as the eluent. This resin removes fromthe mixture unreacted dopamine, dimethylaminopyridine, as well as theliberated DHA molecule. The effluent from the column (a pale yellowsolution) was then evaporated in a rotary evaporator to give a solid.The product was recrystallized from aqueous ethanol (yield=75%).

The structure of compound 8739 (III) was established by massspectrometry. The major peak (95% of the compound) consisted of aproduct with a mass of 550. Fragment analysis by mass spectrometry andcarbon, hydrogen, infrared, and NMR spectra confirmed the structure ofcompound 8739.

A trimethyl silyl derivative (compound IV) of the two hydroxyl groups ofdopamine was also synthesized to further confirm the structure ofcompound 8739. This derivative was shown to have the correct mass of608. ##STR6##

Compound 8739 was stored as a solution in ethanol (12 mg/ml) in thecold. Aliquots of this were evaporated to dryness and dissolved in 15%propylene glycol in 0.1 M NaHCO₃ for use in biological activity tests.

Brain Uptake Studies

A brain penetration index (BPI) determination was used as a criterionfor measuring the capacity of a compound to cross the blood brainbarrier. Shashoua, V. E., Jacob, J. N., Ridge, R., Campbell, A. andBaldessaruni, R. J., J. Med. Chem. 27, 659 (1984). The BPI is a measureof the uptake of a compound by the brain relative to its uptake by theliver. The liver is chosen as a reference since it is an organ which hasno barrier to diffusable molecules present in the blood. Moreover, evenif subcutaneous injections are used, the injected material tends toremain largely at the site of the injection and slowly diffuse into thecirculation. Therefore, the amount of material in the liver will reflectthe amount available rather than the initial dose injected.

Measurements of the quantity of the drug present in the brain and liverwere measured at five minutes after a subcutaneous injection and wereused to calculate the BPI, the equation being:

    BPI=[brain]/[liver]×100

For these measurements, compound 8739 was synthesized from ¹⁴ C-labeleddopamine. Thirty uCi of dopamine labeled hydrochloride was mixed with0.1 mg of unlabeled dopamine hydrobromide and reacted with a two-foldexcess of DHA anhydride. The reaction was run overnight; the product wasthen evaporated to dryness and dissolved in ethanol. The compound wasidentified as 8739 by its migration properties on thin-layerchromatography using chloroform:methanol as one solvent anddimethylformamide (DMF) as the other. The migration properties wereequivalent to those of the unlabeled product.

¹⁴ C-labeled 8739 was dissolved in 15% propylene glycol in 0.1 M NaHCO₃and then injected subcutaneously (s.c.) into male balb C mice (20±2 g).After 5 minutes the animals were sacrificed by cervical fracture and thebrain and liver were dissected out, weighed and homogenized in 8 and 10ml of Brain Protein Solvent (BPS) buffer, respectively [BPS=2% sodiumdodecyl sulfate in 0.03 M Tris, 6 M urea, pH 7.6, 0.01 M EDTA and 0.14 NNaCl]. Aliquots were then counted for ¹⁴ C content in 10 ml of a liquidscintillation fluid, Liquiscent (National Diagnostic Company,Somerville, N.J.) using a Beckman liquid scintillation counter. The ¹⁴ Ccounts were then used to calculate the total quantity of compound 8739present in the brain per gram of tissue as compared to that in theliver. The ratio of the amount in the brain as a percent of that presentin liver was determined.

                  TABLE I                                                         ______________________________________                                        Results                                                                       Compound Brain (cpm/g)                                                                             Liver (cpm/g)                                                                             BPI Value (%)                                ______________________________________                                        8739     1305        4300        30                                           8739     1297        3931        33                                           Dopamine                          4                                           D-glucose                        33                                           ______________________________________                                    

The results indicate that the brain uptake of compound 8739 is overeight-fold higher than the brain uptake for dopamine. Compound 8739 alsocompares favorably with glucose which is reported in the literature tohave a BPI index of 33.

Studies of the Pattern of Distribution of 8739 in Membranes of theCentral Nervous System

The utility of a drug may be determined by its ability to be taken upselectively by the particular regions of the brain upon which the drugacts. A study was made to determine the pattern of distribution ofcompound 8739 in the various membranes in the central nervous system.Approximately 2×10⁶ counts of ¹⁴ C-labeled 8739 in 0.3 ml of 15%propylene glycol in 0.1 M NaHCO₃ was injected subcutaneously into testmice (20±2 g). After 30 minutes the animals were sacrificed by cervicalfracture; the brain was then removed and homogenized in 4 ml of isotonicmedium (0.14 N NaCl, 0.03 M Tris pH 7.4 containing 1.5 mM calciumacetate) according to the method of Whittaker (Whitaker V. P. BiochemJ., 72 694-706 [1959]). The fraction P1 containing nuclear and cellmembrane components was sedimented for 5 min at 2,500 rpm at 0° C. Thesupernatant containing the crude synaptosomal fraction was nextcentrifuged at 13,000 rpm for 30 min to yield a pellet containing thecrude synaptosomal fraction (P2). P1 and P2 were then dissolved in BPS,and the amount of label and protein in each fraction was determined.

                  TABLE II                                                        ______________________________________                                        Results                                                                       CPM/mg Protein after 30 min of Uptake                                                 P.sub.1                                                                       (Nuclear and  P.sub.2                                                 Expt.   Cell Membrane (Crude Synapto-                                         No.     Fraction)     somal Fraction                                                                             P.sub.2 /P.sub.1                           ______________________________________                                        1       2.7           5.2          1.9                                        2       2.7           5.6          2.1                                        3       4.19          12.5         2.9                                        ______________________________________                                    

As shown in Table II, the uptake of compound 8739 into the crudesynaptosomal fraction (P2) was greater by a factor of an average of 2.3than in the P1 fraction (nuclear and cell membrane fraction). Thissuggests that there is a preferential concentration of the compound intothe synaptic fraction P2, indicating that 8739 is more highly associatedwith nerve endings, as would be expected from the natural distributionof DHA in lipid glycerides in such membranes.

Pharmacological Properties Open-field motor activity measurement

The effect of compound 8739 on general motor activity was determined.The general motor activity of balb-c mice was measured in a Stoeltingelectronic activity monitor apparatus during a 90-min period followingan intraperitoneal injection of the compound as a solution in 15%propylene glycol in 0.1 M NaHCO₃. A detailed description of theapparatus is reported in Stewart R. J., Campbell A., Spark G. andBalessarini R. J. Psychopharmacol. 60, 281 (1979).

The test group (six mice) received an i.p. injection of the drug in avehicle (15% propylene glycol in 0.1 M NaHCO₃, a total volume of betweenabout 1-0.3 ml.). The six control mice received the same volume ofvehicle, but no drug. The results (Shown in FIG. 1,) are expressed asthe percent decrease in open field activity for the test group versusthe control group. The results indicate that compound 8739 depresses theactivity of the mice by as much as 50%, demonstrating that compound 8739is biologically active following its uptake into the brain. The responsewas dose dependant with higher doses of compound 8739 resulting in agreater decrease in general motor activity.

Food Consumption Measurements

The effect of compound 8739 on food consumption was determined forbalb-c mice that were food deprived for 24 hr, with water freelyavailable. The six test mice were given an i.p. injection of compound8739 as a solution in 15% propylene glycol in 0.1 M NaHCO₃, a totalvolume of between about 0.1-0.3 ml. The six control mice received thesame volume of vehicle, but no drug. The quantity of "mouse chow" eatenduring the 60-min period following the injections was determined. Theresults, also shown in FIG. 1, are expressed as the percent decrease infood consumption for the test group versus the control group. Theresults indicate that compound 8739 is an appetite suppressant (40-50%decrease in food intake). The decrease was dose dependent, with higherdoses of compound 8739 causing greater decrease in food intake. The sameexperiment was conducted using oral administration of compound 8739. Theresults were the same.

Determination of the Effect of Mode of Delivery of Compound 8739 on OpenField Activity

The effects of the mode of delivery of Compound 8739 (oral vs. i.p.) onthe general open-field activity of mice (n=6) was assessed. As shown inFIG. 2, the drug was as active when ingested as when injected. A 40-50%decrease in activity occurred when either delivery method was employed.No significant changes in open-field activity occurred when either thecarrier molecule (T) or dopamine (DA) is administered at the same dose.

Evaluation of Circling Behavior

Dopamine agonists such as apomorphine and amphetamine cause circlingbehavior in animals with nigrostriatal lesions. Compound 8739 releasesdopamine following proteolysis by central nervous system enzymes. It wasexpected that compound 8739 would cause circling behavior in animalswith nigrostriatal lesions in a manner similar to that of dopamineagonists.

Unilateral nigrostriatal lesions in rats were produced by administeringunilateral injections of 6 OH dopamine into the nigrostriatum pathway.Seven days later, these animals were i.p. injected with the test drugsand circling behavior was recorded as rotations per minute during a30-min period in the test apparatus, Ungerstedt U. and Arbathnott G. W.,Brain Res. 24, 485-493 (1970).

                  TABLE III                                                       ______________________________________                                                          AVERAGE                                                                       ROTATION SCORES                                                      DOSE     (Rotations/minutes)                                         COMPOUND   (mg/kg)    Ipsilateral                                                                              Contralateral                                ______________________________________                                        Apomorphine                                                                              0.1        0.1        4.8                                          "          0.5        0          13.7                                         Amphetamine                                                                              3.0        2.5        0.4                                          "          5.0        3.32       0.92                                         8739       34         0.08       0.05                                         "          51         0.08       0.12                                         Controls   (uninjected)                                                                             0.10       0.12                                         ______________________________________                                    

Apomorphine produced a rapid circling behavior to the contralateral sideof the lesion, whereas amphetamine caused circling rapidly to theipsilateral lesion side. The enhanced contralateral rotations forapomorphine and ipsilateral rotations for amphetamine are consistentwith the reported results for these dopamine agonists. Compound 8739 didnot evoke this behavior. Rather, the rate of circling was very low,approximately the same as that observed for uninjected controls. Thus itappears that compound 8739 does not evoke all of the effects (sideeffects) of dopamine agonists, and therefore, may be considered as a"partial" dopamine agonist.

Self stimulation Data

A self-stimulation test has been used to measure the capacity of a givenpharmacological agent to inhibit rats from receiving self-inducedelectrical stimuli via electrodes implanted in their brains (lateralhypothalamus). Stellar J. R. and Stellar E., The Neurobiology ofMotivation and Reward, Springer-Verlag, New York, 1985. Animals willpress levers to receive a pulse of current from the implanted electrodeat a rate dependent upon the quantity of current that is being deliveredas a reward. It is believed that the reward obtained results from therelease of dopamine caused by the electrical stimulation (Stellar J.R.). The intensity of the currents is varied by raising the frequency atwhich 250 mV pulses (0.1 msec duration) are delivered during a 0.5-sectime span. A plot of the log of the frequency of the delivered pulsesvs. the rate of level press for an animal gives the self-stimulationreward curve. Injections of drugs which have a neuroleptic-type ortranquilizing effect can depress the rate of self-stimulation, shiftingthe response to higher current deliveries. Pemozide can give a depressedrate by about 90%. Investigations of the efficacy of compound 8739 bythis test showed that the compound had no effect on either the reward orthe motor aspect of the self-stimulation parameters. This indicates thatcompound 8739, even though it is able to cause a decrease in the generalmotor activity of an animal, has no effect on the motivation or thecapacity to press for the "current reward". The animal continues topress the lever at the rate equivalent to a non-injected control or onereceiving the vehicle alone. Thus, compound 8739 does not produce yetanother effect (side effect) characteristic of dopamine agonists.

Tests for Tolerance

The effects of daily i.p. injections of compound 8739 at a dose of 20mg/kg on open field activity and food consumption was tested todetermine whether tolerance to the drug was induced over time. The openfield activity of six test mice and six control mice was monitored forfive days. Then, the test mice were given i.p. injections of the drug ina vehicle and the control mice were given i.p. injections of the vehicleonly. This regimen was carried out for a 21 day test period. At the endof the 21 days, the vehicle alone was given daily to both test andcontrol mice and open field activity and food consumption was monitoredfor an additional six days.

FIG. 3 plots the percent decrease in open field activity of the testmice (n=6) as compared to the controls (n=6). As shown in FIG. 3, thelevel of activity prior to injections was the same for both groups. Uponinitation of injections, there was a 30% to 60% decrease in open fieldactivity. This decrease remained fairly constant for the entire 21 daysof injections indicating that no tolerance was induced by repeatedinjections during the test period. Beginning at day 22 and daily untilday 27, vehicle alone was given to both groups. As shown in FIG. 3,activity returned to its predrug level when the drug administration wasdiscontinued.

The effect of long-term administration of compound 8739 on the patternof food consumption of mice was compared to the long-term effects of theadministration of amphetamine. Daily i.p. injections of compound 8739(20 mg/kg) were given to test animals and daily i.p. injections ofamphetamine (2 mg/kg) were given to control animals for 21 days 24 hoursafter the first injection and about every five days after that, theanimals were food-deprived for 24 hours with water freely available, andthen were tested for food consumption for one-hour beginning at fiveminutes after receiving their daily injection.

FIG. 4 plots the percent decrease in food consumption versus time. Foramphetamine injected mice, the decrease in food intake due to theamphetamine virtually disappeared after 15 days indicating completetolerance to the dosage employed. With compound 8739 injected mice, theapproximately 40%-50% decrease in food intake persisted for the entire21 day period indicating no tolerance had developed.

The pharmacological properties of compound 8739 appear to becharacteristic of a partial dopamine agonist. Compound 8739 depressesthe general motor activity and food intake behavior in mice. However,many of the properties which might be considered as "side effects" ofdopamine agonists such as amphetamine and apomorphine are not obtained.Thus, circling behavior in nigrostriatal lesion to animals andmotivational effects in self-stimulation experiments do not resultfollowing the administration of compound 8739.

Compound 8739 may be administered orally without any apparent loss inefficacy, and, therefore, is stable. Moreover, the compound does notbind to the dopamine receptors in receptor binding assays. Thus, thedrug appears to be inactive until proteolysis releases the activedopamine. While the mechanism of action of the drug is not fullyunderstood, and the inventor does not intend to be bound by any theory,it is believed that the localization of uptake into synaptic endings maycause site specific release of the active dopamine from the prodrug.Such site specific release could be responsible for some of thefavorable properties of the drug. Further, that the carrier and drug arenatural constituents of the CNS may contribute to compound 8739'sdesirable properties.

The invention is not limited to the foregoing description of thepreferred embodiment. Thus, it is contemplated that the specific carrierdescribed in the preferred embodiment and other carriers of theinvention described in greater detail below are capable of being linkedby an amide bond or otherwise to other neurotransmitters, analogues ofneurotransmitters including analogues of dopamine and other neuroactivesubstances to facilitate the delivery of the substance across the bloodbrain barrier and into the CNS. The list of such neuroactive substancesis well known to those skilled in the art and includes, but by no meansis limited to: neurotransmitters such as dopamine, serotonin, γaminobutyric acid, norepinephrine, histamine and epinephrine;neuroactive amino acids acids such as glycine, aspartic acid, glutamicacid and taurine; and anorectic compounds such as amphetamine,phefluoramine, and diethylpropion. Although the CNS uptake of theanorectic compounds is satisfactory, when these compounds are coupled tothe preferred carriers localized delivery of these compounds into thesynaptosomal membranes of the CNS is facilitated.

Amide bonds are preferred because they may survive the environment ofthe stomach and the prodrug may be administered orally. However, itshould be recognized an ester bond may be used to link the carrier ofthe invention and a drug, with the resulting conjugate capable ofcrossing the blood brain barrier. Such a prodrug may be injected orprotected from the environment of the stomach by, for example, coatings,well-known to those skilled in the art. Such a coating may be called foreven in the presence of an amide bond between the carrier and the drug.

The compounds of the invention can be prepared in pharmaceuticalpreparations containing the compounds themselves and a pharmaceuticallyacceptable carrier. This pharmaceutically acceptable carrier may besolid or liquid. Examples of liquid carriers include water, an aqueoussolution of non-toxic salts, such as sterile physiological solutions ofsaline, or aqueous solutions containing organic solvents, such asethanol. Also suitable are emulsions, such as oil--in--water emulsions.Solid carriers include both nutritative carriers, such as sucrose orgelatin, and non-nutritative carriers, such as cellulose or talc.

Slow-release capsules and other protective means are suitable for theoral administration of the compounds of the invention due to theprotection afforded against hydrolysis in the gastrointestinal tract.Preferred are those capsules which permit the compounds to bypass thestomach. When the present compounds are to be administered peritoneally,they can be administered by subcutaneous, intramuscular or intravenousinjections.

Amounts of the compounds of the invention useful for promoting theuptake of the drug by the brain may vary from individual to individual,as well as varying from the particular disorder being treated and theparticular effect desired. Such amounts can be determined byexperimentation as is well understood by those skilled in thepharmaceutical arts. For suppressing appetite with Dopamine conjugates,amounts in the range of about 100-20,000 micro grams per kilogram bodyweight are preferred.

Generally, compounds are most active when administered intravenouslythan by the other preferred routes. However, when an amide bond is usedto conjugate the drug and carrier, oral administration of the drugappears to work quite well. In any event, when the conjugates of theinvention are used to promote the uptake of a drug into the centralnervous system, they are administered to humans in amounts sufficient topromote the crossing of the blood brain barrier. When the therapyinvolves restoring a deficiency of a neuro-transmitter in a human, theconjugate is administered in an amount sufficient to cause thenormalization of the deficiency. When the compounds of the presentinvention are used for treating Parkinsonism or hyperprolactinemia orfor suppressing appetite, then they are administered to a human in needof such treatment in an amount sufficient to affect the desired result.

Administration, of course, may be made by any method which allows theactive compound to reach the bloodstream and penetrate through the bloodbrain barrier. Typical methods include oral, rectal, peritoneal andtopical administration of the compounds. When the compounds areadministered orally, the composition can be in the form of dragees,tablets, syrups or ampules. When the compounds are administeredrectally, the composition can be in the form of a suppository. Inaddition, when the compounds of the invention are to be administered bytopical application, they can be in the form of pomade or a gel.

The ability of the bond between the drug and the carrier to be brokenonce the prodrug is in the CNS will influence the choice of bonds.Likewise, the desired delivery site in the CNS may affect the choice ofbonds as the enzymes responsible for breaking various bonds areconcentrated in particular locations.

Variations of the particular carrier described in the preferredembodiment also are contemplated. For example, it has been found that astraight chain fatty acid that does not occur naturally in the brain andhaving 12 carbon atoms and no double bonds coupled to dopamine does noteffectively cross the blood brain barrier and is completely inactive asan appetite-suppressant. Likewise, another straight chain fatty acidthat does not occur naturally in the brain and having 22 carbon atomsand no double bonds coupled to dopamine does not effectively cross theblood brain barrier and is essentially inactive as anappetite-suppressant. However, a straight chain fatty acid occurringnaturally in the brain and having 18 carbon atoms and 3 double bondscoupled to dopamine is partially active. This molecule crosses the bloodbrain barrier, and it has some effect on locomotor activity although nosubstantial effect on appetite. Thus, it appears that the length of thefatty acid, the degree of saturation and whether the fatty acid isnaturally occurring in the brain affects the ability of the carrier tobe combined with a drug to form a prodrug that will cross the bloodbrain barrier and effectively deliver and liberate the drug at an activesite. The carrier molecule preferably is a straight-chained fatty acidof between 16 and 26 carbon atoms in length. More preferably the carriermolecule is between 16 and 22 carbon atoms in length and occursnaturally in the brain. Among the fatty acids occurring naturally in thebrain are those with 16 carbon atoms and 0, 1 or 2 double bonds (C16:0;C16:1 and C16:2), those with 18 carbon atoms and 1, 2 or 3 double bonds(C18:1; C18:2; and C18:3), those with 20 carbon atoms and 1, 2 or 4double bonds (C20:1; C20:2; and C20:4) and those with 22 carbon atomsand 4, 5 or 6 double bonds (C22:4; C22:5 and C22:6). While the positionof the double bonds may be between any of the carbon atoms in the fattyacids, the preferred loci are those which occur naturally in the fattyacids of the CNS. Among the naturally occurring fatty acids, C16:0 andC22:6 are preferred due to their preference for concentrating in thesynaptosomal membranes, with C22:6 most preferred.

In addition to the foregoing fatty acids, branched chain fatty acidshaving between 16 and 26 carbon atoms may be used, such as for example,the foregoing naturally-occurring fatty acids with methyl, ethyl andisopropyl groups at various positions along the carbon chain. Particularexamples include analogues of the naturally occurring polyisoprenoids(dolicols) such as ##STR7##

Having now fully described this invention, it will be appreciated bythose of ordinary skill in the art that the same can be practiced with awide and equivalent range of compositions, modes of administration,therapeutic treatments and the like, without affecting the spirit orscope of the invention or any embodiment thereof.

What is claimed is:
 1. A method for suppressing appetite in a patientcomprising, introducing into the patient a prodrug comprising a fattyacid coupled to dopamine.
 2. A method for suppressing appetite asclaimed in claim 1 wherein the prodrug is introduced into thebloodstream of the patient.
 3. A method for suppressing appetite asclaimed in claim 1 wherein the fatty acid is a fatty acid naturallyoccurring in the brain.
 4. A method for suppressing appetite as claimedin claim 1 wherein the prodrug comprises a fatty acid having between 16and 26 carbon atoms.
 5. A method for suppressing appetite as claimed inclaim 4 wherein the prodrug is selected to have a BPI index of at leasttwo times the BPI index of dopamine.
 6. A method for suppressingappetite as claimed in claim 1 wherein a prodrug comprising a fatty acidcoupled to dopamine via a bond capable of being hydrolyzed in the brainis introduced into the patient.
 7. A method for suppressing appetite asclaimed in claim 1 wherein a prodrug comprising a fatty acid coupled todopamine via a bond capable of surviving the environment of the stomachis introduced into the patient.
 8. A method for suppressing appetite asclaimed in claim 1 wherein a prodrug comprising a fatty acid coupled todopamine via an amide bond is introduced into the patient.
 9. A methodas claimed in claim 1 further comprising first forming a prodrugcomprising a fatty acid coupled to dopamine.
 10. A method as claimed inclaim 1 further comprising, first forming a prodrug by coupling a fattyacid to dopamine, andthen forming a pharmaceutical dose containing theprodrug prior to introducing said prodrug into the patient.
 11. A methodfor suppressing appetite as claimed in claim 1 wherein a prodrugcomprising a fatty acid selected from the group consisting of:C16:0;C16:1; C16:2; C18:1; C18:2; C18:3; C20:1; C20:2; C20:4; C22:4; C22:5;and C22:6 coupled to dopamine is introduced into a patient.
 12. A methodfor suppressing appetite as claimed in claim 1 wherein a prodrugselected from the group consisting of ##STR8## wherein D is dopamine, isintroduced into a patient.
 13. A method for suppressing appetite asclaimed in claim 55 wherein the prodrug ##STR9## is introduced into apatient.
 14. A method for suppressing appetite as claimed in any ofclaims 1, 11, 12 or 13 wherein a prodrug comprising a fatty acid coupledby an amide bond to dopamine is introduced into a patient.
 15. A methodfor suppressing appetite in a mammalian host comprising administering toa mammal a pharmaceutically effective amount of a prodrug comprising afatty acid coupled to dopamine.
 16. A method as claimed in claim 15further comprising first forming a prodrug by coupling a fatty acid todopamine.
 17. A method for suppressing appetite as claimed in claim 16wherein a prodrug comprising a fatty acid selected from the groupconsisting of: C16:0; C16:1; C16:2; C18:1; C18:2; C18:3; C20:1; C20:2;C20:4; C22:4; C22:5; and C22:6 coupled to dopamine is administered to amammal.
 18. A method for suppressing appetite as claimed in claim 17wherein the prodrug selected from the group consisting of ##STR10##wherein D is dopamine, is administered to a mammal.
 19. A method forsuppressing appetite as claimed in claims 1, 11, 12, 13, 15, or 18wherein the prodrug is administered with a pharmaceutically acceptablecarrier.
 20. A method for suppressing appetite as claimed in claim 19wherein the pharmaceutically acceptable carrier is a capsule.
 21. Amethod for suppressing appetite as claimed in claim 19 wherein thepharmaceutically acceptable carrier is a carrier which permits theprodrug to bypass the environment of the stomach.
 22. A method forsuppressing appetite as claimed in claim 20 wherein the capsule is aslow release capsule.
 23. A method for suppressing appetite as claimedin claim 19 where the pharmaceutically acceptable carrier is a tablet.24. A method for suppressing appetite as claimed in claims 1, 11, 12,13, 15, or 18 wherein the dopamine is administered in a dose betweenabout 100 to about 20,000 micrograms per kilogram of body weight.
 25. Amethod for suppressing appetite as claimed in claims 11 or 17 whereinthe fatty acid is naturally occurring in the brain.